Where the hell did that water spout come from?

Lennox Head has been declared a natural disaster zone by NSW Premier Kristina Keneally, after a tornado tore through the town yesterday. But how does a tornado happen, and why so quickly? Crikey spoke to the Australian Bureau of Meteorology’s Andrew Haigh to find out.

Were they tornadoes or water spouts?

When tornadoes form over the water they are often called water spouts.

How did the tornado occur?

Tornadoes are rapidly rotating columns of air, which usually form under thunderstorm clouds, but occasionally, particularly over the water, they can form under smaller clouds. The tornadoes at Lennox Head formed under a thunderstorm cloud, which started over the water and moved over land, where it caused a large amount of damage.

The tornado was associated with a particularly well organised thunderstorm, known as a super cell.

Are they hard to predict?

The tornado formed at the same time the thunderstorm had formed, so by the time we picked it up on radar it was too late to send a warning. Once we had reports of Lennox Head, we issued a severe thunderstorm warning. The tornado was also very small in size and they are unusual this time of year, which made it difficult to predict.

We already had a severe weather warning for heavy rain and flash flooding for a large area.

How fast were the water spouts?

We don’t know for sure, but the damage in Lennox Head indicates, and there is widespread agreement within the bureau, that winds where at least 150 kmh.

What stops them?

The smaller a weather feature is the shorter the time it tends to last for. The low-pressure system responsible for NSW weather, currently, is an example of a feature which has been typically for the past few days and is hundreds of kilometres wide. While the tornado, which was 50 metres to 100 metres wide, only lasted a few minutes.